1. Field of the Invention
The present invention relates to an internal antenna for a mobile handset and, particularly, to a planar inverted F antenna (PIFA), which is a type of the internal antenna for a mobile handset. By using the internal antenna of a mobile handset according to the present invention, the broad bandwidth can be obtained without increasing space for inclusion of a general small-size dual band PIFA.
2. Prior Art
As there is great increase in the use of mobile handsets, researches are conducted actively on antennas for the purpose of raising reception sensitivity of wireless signals. Ordinarily, a PIFA has acceptable characteristics in terms of the Specific Absorption Rate (SAR), a standard to measure damage of microwave to human body, and is easy to be included in a light, thin, simple and small mobile unit. Thus, such PIFA is generally used in a mobile handset.
FIG. 1 illustrates a PIFA. As shown in FIG. 1, the PIFA has structure where a radiating patch 1 is attached to a short pin 3 protruded on a ground plate (GND) and a feeding pin 5 is connected to the radiating patch 1. The radiating patch 1 receives power supply through the feeding pin 5 and is short-circuited with the GND by the short pin 3, thus accomplishing impedance matching. Accordingly, given relevant operating frequencies, the PIFA is designed by adjusting a length L of a patch and a height H of the antenna according to a width Wp of a short pin 3 and a width W of the patch.
In such PIFA, of the entire beam generated by a current induced in the radiating patch, beam directed to the GND is re-induced and the beam directed to the human body is attenuated. Thus, SAR characteristics are improved and the beam induced to the direction of the radiating patch 1 is strengthened, so that the PIFA has advantages in that the PIFA has desirable directivity and it may decrease a size of the antenna.
On the other hand, as service providers utilize various frequency bands, the PIFA in a dual band antenna type (Hereinafter, dual band PIFA) that may utilize different frequency bands is being developed actively. FIG. 2 illustrates a dual band PIFA.
As shown in FIG. 2, the dual band PIFA is designed such that a radiating patch 10 has the spur line and thus includes a first patch portion 12 and a second patch portion 14, that have different lengths and widths. The first patch portion 12 and the second patch portion 14 are fixed to a short pin 3 which grounds the radiating patch 10 and receive power supply from a feeding pin 5.
Even though the first patch portion 12 and the second patch portion 14 make up the same radiating patch 10, they are distinguished into two different radiating patch domains and resonate at different frequency bands. Thus, the first patch portion 12 and the second patch portion 14 may operate at two different frequency bands. Here, the relevant frequency bands at which the respective patch portions 12, 14 operate may be changed by adjusting the respective lengths L1, L2 of the patch portions.
In these conventional PIFAs, however, the relevant bandwidths used by such PIFAs are generally narrow and thus the conventional PIFAs are not adequate for the use in the personal communication service (PCS) or cellular frequency band, for which the demand is increasing daily. Further, if the lengths of patch portions (e.g., L1, L2) are increased in order to broaden the bandwidth, the antenna would become too large to be included inside of a mobile handset.